1. Field of the Invention
The present invention generally relates to a method for forming a semiconductor structure to suppress a hot cluster, a method for suppressing a hot cluster and a semiconductor structure for suppressing a hot cluster. In particular, the present invention is directed to a semiconductor structure with a dopant gradient region of a constructed back diffusion type as well as an isolation doping region surrounding a shallow trench isolation so that in the resultant semiconductor structure a shallow trench isolation region is substantially adjacent to the dopant gradient region to suppress a possible hot cluster in the semiconductor structure.
2. Description of the Prior Art
A CMOS image sensor is widely used in many applications, such as a portable device, a web cam, a monitor, a toy or a medical instrument. Like any other successful consumer electronic product, a successful CMOS image sensor must have high sensitivity to gain the upwind side of the very competing market.
As far as the high sensitivity is concerned, one of the most critical questions is the failure owing to a hot cluster. A hot cluster failure is like a contagious disease, not only the functions of the original pixel are destroyed but also the neighboring pixels are also suffering collateral damages so that normal ones and abnormal ones together become bad ones. These bad pixels collectively form a cross shape cluster or a block shape cluster due to the hot cluster failure.
Since the current product standards are demandingly high, only one single hot cluster failure results in the total failure of the die, no matter how good the others are. The bottle neck to solve the hot cluster failure is: there may be various reasons from every manufacturing step and they are generally fab-related. So far the proposed ways to solve the hot cluster failure problems are still limited to case-by-case approaches. There is no universal and thorough solution available.